Method and apparatus for determining the location of the edge of a ribbon of glass under production in a metal flotation furnace

ABSTRACT

Method and apparatus for the accurate determination optically, of the location at one or more selected positions, of the edge of an incipient ribbon of glass being produced in a metal flotation furnace. A scanning periscopic telescope responsive to infrared rays has its objective end within the furnace adjacent to and above the edge of the ribbon at the selected location. The telescope is mounted for horizontal axial translation in a direction generally transversely of the edge of the ribbon. In normal position the objective is directly over the edge of the ribbon at a location critical to control of the furnace. When for any reason the edge of the ribbon shifts in a direction generally transverse to its direction of motion on the molten metal, the energization of two photoelectric cells incorporated in the telescope, is correspondingly varied. A follow-up motor mechanically connected to axially translate the telescope is thereby correspondingly and uniquely energized to restore the objective to its position directly over the edge of the ribbon. The translation thus effected is repeated at a remote control point or station to thus indicate the exact position of the edge of the ribbon at the critical location, thus enabling precise control of the furance. A number of the instruments may be located at spaced intervals along each edge of the ribbon.

United States Patent [191 Goerens et al.

[ Apr. 16, 1974 METHOD AND APPARATUS FOR Primary Examiner-James W. Lawrence DETERMINING THE LOCATION OF THE Assistant Examiner-Davis L. Willis EDGE OF A RIBBON OF GLASS UNDER PRODUCTION IN A METAL FLOTATION [57] ABSTRACT FURNACE Method and apparatus for the accurate determination [75] Inventors: Paul Goerens, Paris, France; Heinz p y of the at one or more Selected P p Landkreis Aachen, Germany tions, of the edge of an incipient ribbon of glass being produced in a metal flotation furnace. A scanning [73] Asslgnee: samt'cnbam Indusmes periscopic telescope responsive to infrared rays has its 22 Filed; June 3 1971 objective end within the furnace adjacent to and above the edge of the ribbon at the selected location. [21] Appl' 149,742 The telescope is mounted for horizontal axial transla- R l d U s Application Data tion in a direction generally transversely of the edge of [63] continuationdmpart of sen 73 024 Sept. 17 the ribbon. In normal position the objective is directly 1970, abandone over the edge of the ribbon at a location critical to control of the furnace. When for any reason the edge [30] Foreign Application priority Data of the ribbon shifts in a direction generally transverse Sept 18 1969 France 69 31756 to its directlon of motion on the molten metal, the energization of two photoelectric cells incorporated in 52 US. Cl. 250/342 telempe is cwespmdingly A 51 Int. Cl. G0lt 1/16 meihanicany nnected axially translate the [58] Field of Search 250/833 H, 219 WD, telescope is thereby correspondingly and uniquely en- "is'd' LG 219 TH 342 erglzed to restore the ob ective to its position directly over the edge of the ribbon. The translation thus effected is repeated at a remote control oint or station [56] References cued to thus indicate the exact position of Fhe edge of the UNITED STATES PATENTS 1 ribbon at the critical location, thus enabling precise 3,519,825 7/1970 LOCKS 250/833 H control of tha furance A number of the instruments may be located at spaced intervals along each edge of run on e a 2,931,917 4/l960 Beelitz 250/219 WD the ribbon 19 Claims, 7 Drawing Figures [6 l\ 5 3o l 2 22 L 4 6 u G as KT l 5 |2 |o" 23 l3 PATENTEUAPR 15 I974 SHEET 1 OF 3 I2 IO FIG.|.

A INVENTORS Paul Goerens 8 Hemz Po pe ATTORNEYS FlG.-5.

METHOD AND APPARATUS FOR DETERMINING THE LOCATION OF THE EDGE OF A RIBBON OF GLASS UNDER PRODUCTION IN A METAL FLOTATION FURNACE CROSS REFERENCE TO RELATED APPLICATION This application is a continuation in part of application Ser. No. 73,024, filed Sept. 17, 1970, now aban' doned.

BACKGROUND OF THE INVENTION In the production of sheet glass by molten metal flotation, molten glass is deposited at a controlled rate onto the molten metal, usually tin, at one end of the flotation tank or furnace. The glass spreads out into the form of a flat ribbon as it is drawn along on and over the surface of the molten tin. The temperature of the ribbon is gradually reduced as it travels toward the exit end of the furnace, so that it can be gripped without damage thereto at the point of emergence.

Because of the high temperatures involved the flotation furnace must be completely enclosed so that direct visual inspection of the incipient ribbon is impossible. Nevertheless it is very important to production 'of glass of the required width and thickness, to know the position of the edges of the ribbon on and with respect to the supporting surface of the metal, at certain critical points along their lengths.

The present invention solves the problem by novel optical means which, continuously or intermittently observes the edge of the glass ribbon and in response to a change in illumination or energization of two photoelectric cells created only when the edge shifts generally transversely to its direction of motion along and over the surface of the molten metal, controls follow-up power means connected to the optical means, to maintain or to restore such optical means to its former definite position over the observed edge. The power means also operates indicating means at a remote station and thus affords a measure of the direction and distance of shift. For if this rate is too high, for instance, the excess of heat will result in highly undesirable variations in thickness of the sheet glass ultimately produced. When first deposited onto the molten tin at the upstream end of the furnace, the glass spreads out evenly to a maximum width which may be substantially equal to the width of the molten tin bath. Then as it is-drawn along the incipient ribbon gradually contracts to essentially its desired final width. One highly critical and important location is that at which the sheet or ribbon approaches its maximum width as aforesaid; and it is therefore very desirable that the width of the ribbon at this location be maintained essentially constant. This means, simply, that a plane normal to the direction of travel of the ribbon, at the critical location, should intersect the two edges thereof, in points having a constant distance of separation.

Since the tangents to the two edges of the ribbon at such points make small acute angles with the direction of travel, it will be understood that the direction of translation of the optical means thereat will be nearly perpendicular to such tangents, respectively. Hence it is not required that the direction of translation of the optical means be exactly perpendicular to the direction of travel of the ribbon, at such points.

DESCRIPTION OF THE PRIOR ART Several types of apparatus have been proposed for observing or determining the location of the edges of the incipient glass ribbon within the flotation tank or furnace. For example it has been suggested to use electrodes for this purpose. But these are always subject to erosion because of the intense heat to which they are unavoidably subjected. It is difficult to compensate for errors in readings otherwise introduced by such erosion. Furthermore such electrodes must be in physical contact with the molten glass and even if they are of a material such as graphite, which is not wetted by the glass, they soon become fouled with glass or other encrustations adherent thereto. Such electrodes can also seriously disturb the necessary smooth even flow of glass on the surface of the metallic bath. Other kinds and types of devices, electrical in nature, for detecting the location of the edges of the incipient ribbon have been proposed. But all of them inherently involve difficulties and drawbacks which render them impracticable.

In another form of apparatus for the present purpose it has been proposed to use pneumatic effects such as small differential changes in pressure. However, such devices have a very weak or low sensitivity because the edge of the incipient sheet varies over an appreciable distance transversely of the sheet, from normal thickness to a thin knife-like edge. Hence with such devices the position or location of the edge of the ribbon can vary to an undesirable extent before such variation is sensed. Also, since such pneumatic devices must have their sensitive elements located closely adjacent to the glass, they also create undesirable perturbations and imperfections in the flowing glass.

In the above type of device it has been proposed to use successive soundings with alternate immersion and retraction. But such devices involve excessive complications and are, moreover, difficult to operate within .the intensely heated furnace enclosure.

To overcome the difficulties and drawbacks above set forth, apparatus involving direct visual observation might have been proposed. Experience shows however that it is difficult to spot precisely the outer limits of the line of demarcation of the glass on the surface of the molten metal. Therefore such direct observation devices do not adequately solve the problems. This may be explained by the fact that the furnace is necessarily completely enclosed and contains the glass and tin at about the same temperature. The glass and tin form two surfaces of small visual difference and located closely adjacent to the roof of the furnace, which has a low height. The glass remains essentially transparent even though its temperature is of the order of 600 to l,l00 C., so that as a result optical devices of the type involving direct visual observation make it difficult to distinguish between the glass and the underlying metal or supporting bath. Further, the thickness of the glass at and along its edge may vary over a width or band several centimeters wide. Since the glass varies progressively in thickness, transversely of this edge band, from normal to zero, an optical effect is created which makes it very difficult to determine the exact position of the edge of the ribbon.

SUMMARY OF THE INVENTION In accordance with the present invention, observation of the edges of the glass ribbon is effected by rays having wavelength of between 4 and 8 microns. The properties of the tin and the glass supported thereon are notably different optically in the aforesaid range. In particular the glass is essentially opaque to wavelengths in this region of the spectrum and therefore the surface of the tin is essentially invisible through the molten glass. Thus observation is under optimum conditions in the range of wavelengths noted, and it is possible to determine under these very favorable conditions, the line of demarcation between the edges of the glass ribbon and the underlying bath of molten tin. Thus in conformity with the invention, as subsequently described, observation and detection of the edges of the glass ribbon is effected by an optical instrument having a sensitivity range between about 4 and 8 microns.

It is preferable to provide a cold wall in front of this zone of observation, that is, at the objective end of the instrument. Such a feature calls for a telescope of ample size having a narrow field and capable of observation of the glass at an angle normal to its surface.

Thus the telescope embodying the invention is preferably of periscopic form. The periscope is jacketed in the interior of va double-walled tube through which cooling fluid may be circulated. The telescope has an observation orifice in its inner end. Its tube is mounted to pass outwardly of the furnace through an air-tight aperture in the wall thereof. The telescope is mounted so that it may be adjusted as to depth of penetration into the furnace in the direction parallel to the plane of the incipient glass ribbon and substantially but not necessarily precisely, normal to its direction of travel on and over the molten metal. Suitable means for the telescope for thus mounting it, are disclosed in U.S. Pat. No. 3,649,237. Such means enables the telescope and its field of view to be displaced substantially transversely of the direction of movement of the ribbon of glass, over a distance sufficient to encompass all possible variations or changes in location of the edge of the ribbon.

An important feature of the invention is the optical system assembly. In particular the objective opening thereof within the furnace is equipped with means to discharge over and about the objective, a moving curv tain of inert gas such as nitrogen, which aids in cooling the objective end and prevents the escape of tin vapor so that it cannot condense on the various optical surfaces and elements of and within the telescope.

The apparatus forming the present invention may be located at any preselected point along the ribbon. But in commercial operation the location of greatest interest and criticality, in particular, for proper regulation and control of the furnace, is the zone where the incipient ribbon attains or approaches its maximum width, as has been previously explained. In this zone any changes in width will be essentially at the fastest rate. The range of width changes during fabrication depends, of course, upon the precision with which the furnace is regulated, but should not exceed i 10 cm at each edge or border of the ribbon. A pair of telescopes embodying the invention are used, one to observe each edge, respectively, at directly opposite locations. The variations in transverse position of the edges of the incipient ribbon differ with different types, kinds and compositions of glass under manufacture.

While it is contemplated that the field of view of the instrument embodying this invention may be made of such dimension parallel with the optical axis, as to embrace all possible locations of the edge of the ribbon, in which case the telescope may be fixedly mounted, in actual practice there are so many factors which may cause excessive lateral displacement of the edges of the ribbon, that a fixed field of view will not be ample to cover all lateral displacement positions. Hence adjustment of the telescope transversely of the edge of the ribbon and parallel with its plane, is preferable.

For instance, a series of spaced cells linearly arranged in a direction generally transverse to the image of the edge of the ribbon may be so disposed that each controls a respective one of a plurality of contiguous indicators so that the location of the edge may be determined by visual comparison of the readings of the several indicators. Or a single cell may be movably mounted in the aforesaid direction, by a follow-up motor which it controls in an on-off circuit, to thereby maintain the cell in a null position corresponding to the instantaneous location of the edge of the ribbon.

Such apparatus is mobile and compact but the small height of the furnace above the level of the molten metal therein, prevents placement of the axis of the periscope more than fifteen centimeters above the level of the bath of tin. This fact requires a telescopeof relatively large apex angle and creates problems of depth of field, sensitivity, and protection from heat of the forward or objective optical elements. The complications thus created are ordinarily too great for the required sensitivity.

We have discovered that it is more advantageous to provide a reflector at the objective opening of the instrument, such as, preferably, a planar mirror of stainless steel positioned for example, across the axis of the telescope tube, to receive rays from a narrow orifice in the wall of the tube. This reflector is associated with a positive ocular transparent to infrared rays and an assemblage of two photoelectric cells arranged parallel and located in the image plane of the system. The image of the observed edge of the ribbon of glass normally falls between the two cells in a line essentially parallel with themso that they are rendered variably sensitive to a displacement of this line.

The differential illumination is sufficiently clear and pronounced to enable measurements of changes in position of the line of the order of less than 1 millimeter. To facilitate amplification of the effective signals it is proposed to directly modulate the luminous rays by a toothed disk rotating before the cells and effecting an apparent sinusoidal signal therefrom. The smallness of the field of view of the apparatus prompts an optical system which is displaceable or translatable as a unit in the direction generally perpendicular to the edge of, and to the direction of travel of, the incipient ribbon of glass.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows in side elevation the general arrangement of the apparatus in relation to the contiguous portion of the furnace and a ribbon of glass being formed FIG. 2b is a horizontal axial section to the same scale as FIG. 2a, showing the ocular end of the telescope and in particular the photoelectric cells, their mounting, and the rotary toothed disk positioned between them and the source of rays;

FIG. 3 is a transverse section to about the same scale as FIGS. 2a and 2b, taken in a plane identified by line 3 3, FIG. 2b;

FIG. 4 is a schematic view showing the circuitry of the instrument;

FIG. 5 is a detail sectional view taken in plane identified by line 5 5, FIG. 1; and

FIG. 6 is a detail schematic showing the circuitry for control of the follow-up motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring in particular to FIG. 1, a portion of the furnace wall is indicated at 1, having therein an opening 2 through which passes the forward or objective end of a cylindrical telescope tube 3. The end of this tube exteriorly of the furnace is mounted within supporting rings 4 and 5 fixed thereto and each of which has a pair of collars apertured to slidably fit a-pair of guide rods. For example, referring to FIG. 5, the guide rods 6, 7 are mounted in fixed, laterally-spaced parallel relation on a frame generally indicated at 8. The collars for ring 5 are shown at 9 and 10. A threaded rod 11 is journaled I on frame 8 between and parallel with rods 6, 7 and is engaged by a nut element 12 fixed with the telescope tube 3. The threaded rod has one end connected with the shaft of a follow-up or servo-motor 13. Thus in a way clear from inspection of FIGS. 1 and 5, turning of the shaft of motor 13 in one direction or the other effects a corresponding smooth guided translation of the telescope on and along the rods to thereby vary the depth of penetration of its objective within the furnace.

Tube 3 is provided with a seal shown as a flexible bellows sleeve 14, FIG. 1, having one end attached to a collar 15 surrounding and slidably fitting the tube. The other end of sleeve l4'is clamped at 16 to the rim of a fitting 17 attachedto the wall of furnace 1, about aperture 2. The detachable fit between the telescope tube and collar 15 adapt the mounting for different telescopes and different types of fabrication.

At 18, FIG. 1 is identified the objective opening in the end of tube 3 within the furnace, wherein it is seen to be directly above the contiguous edge of a ribbon of glass G under production, and floating on a bath T of molten tin.

Referring to FIGS. 2a, 2b and 3, an intermediate tube 19 extends coaxially in and along tube 3 in radiallyspaced relation therewith, to define a cooling chamber or jacket 20, closed at its other end by a ring 21, FIG. 2b. Cooling fluid introduced into chamber 20 by pipe '22 flows through the chamber and is exhausted by pipe 23. Baffles 24 positioned within the chamber assure that the coolant flows completely about the walls and inner end of the telescope tube before being exhausted at 23.

An inner tube 25 ismounted within and coaxially of intermediate tube 19. At its inner end this tube 25 is mounted to an annular shoulder on ring 26 and which in turn, has a smooth accurate fit within a centering sleeve 27 attached to the interior wall of tube 19. At its other or outer end, tube 25 is provided with a flange 28 by which it is attached to ring 21. The two radiallyspaced tubes 19 and 25 thus form a chamber 29 into which an inert cooling gas such as nitrogen is introduced by pipe 30. The gas passes inwardly along chamber 29 and in a manner clear from FIG. 2a, exits through objective opening 18. Apertures 31 provided in the wall of tube 25 enable a portion of the nitrogen to enter the interior thereof. Such portion may exhaust through an aperture 32 which, as shown, is directly above objective opening 18 in tube 3. Nitrogen may also pass from the interior of tube 25 through other or auxiliary openings such as 33.

A support block 34 is fixed within an opening in ring 26. The opening is closed by plate 35. A reflector which may be of stainless steel and indicated at 36, is mounted to the surface of block 34 extending at 45 to the plane determined by the intersecting lines, one vertical centrally through openings 18 and 32, and the other coincident with the longitudinal axis of tube 25. Thus, rays emanating from the interior of the furnace pass vertically through openings 18 and 32 and, by reflector 36 are deflected outwardly along the axis of tube 25.

The rays are concentrated by fluorspar or fluorite lens system 37 from whence they pass to and through a filter 38 which is transparent only to radiant energy of more than 4 microns wavelength. The filter is mounted within a central or axial opening in a disk 39. This disk as is apparent from FIG. 2b, is fixed with and closes one end of mounting 40 for lens system 37. The

v mounting is axially slidable within and along tube 25.

Disk 39 has a rod-like extension 41 which passes outwardly along tube 25 in radially offset relation with respect to the axis thereof, and traverses an opening in mounting block 42. The free end of extension 41 is threaded so that adjustment of filter 38 and lens system 37 along tube 25 can be effected by nuts 43 screwed thereon.

Photoelectric cells 44 and 45 are in rectangular form as shown upon FIG. 3 and are spaced by and between insulating plates 46 and 47 fixed in mounting 48, in turn carried by block 42 previously described. This block has a bore 49 parallel with and radially offset from the optical axis of the instrument, that is, the central longitudinal axis of tube 25. Bearings 50, 51, FIG. 2b, spacedly mounted in and along bore 49, journal a shaft 52.

Shaft 52 is connected by a separable coupling to the shaft of a synchronous motor 54. The other end of shaft 52 has a toothed disk 55 fixed thereon. The disk has regularly-angularly-spaced radial openings 56 as shown by FIG. 3. From FIGS. 2b and 3 it is noted that disk 55 is so positioned that on rotation thereof it periodically intercepts rays from filter 38 otherwise continuously incident upon the region of cells 44 and 45. The rate of interception is constant and, of course, equal to the number of openings 56 times the r.p.s. of the disk. Cells 44 and 45 are of a known type essentially nonresponsive to rays having a length above about 8 microns.

OPERATION Referring to FIGS. 4 and 6, when normal operating condition is extant the contiguous edge of the incipient ribbon of glass G is directly below reflector 36 as depicted on FIG. 4. Under such condition cell 45 only is energized and the output thereof, amplified and rectified as at 60, 62, 64 and 66, energizes relay 68 so that contact 68a is opened and contact 68b is closed. Since at this time relay 67 under control of the output of cell 44, is de-energized, its contact 67a is closed and that at 67b is open. Thus there is no energization of solenoid 70b of motor reversing relay switch 70 and motor 13 remains at rest.

When the edge of glass ribbon G moves to the right as viewed upon FIG. 4, the luminous intensity effective on the cells is increased. Under this condition cell 44 is energized and cell 45 remains energized as in the previous paragraph. The output current of cell 44, amplified and rectified at 59, 61, 63 and 65, energizes relay 67 thus closing contact 67b and opening contact 67a. Since contact 68!; remains closed, a circuit is completed through solenoid 70b of motor reversing relay switch 70 and in a way obvious from inspection of FIG. 6, motor 13 is energized. The resulting direction of rotation is such as to axially shift telescope tube 3 to the right until normal position of reflector 36 directly over the edge of the ribbon of glass G, is restored, and cell 44 again becomes de-energized and rotation of motor 13 ceases.

When the edge of glass G moves to the left, as viewed upon FIG. 4, both cells 44 and 45 are subject to a reduced intensity of radiant energy which is insufficient to render either of them conductive. Under such condition both relays 68 and 67 are de-energized and the condition shown upon FIG. 6 is extant wherein coil 70a of reversing switch 70 is energized and motor 13 rotates in a reverse direction from that previously described. This reverse direction of rotation axially shifts the telescope 3 to the left, to again restore reflector 36 to a position directly over the contiguous edge of the ribbon, resulting in de-energization of follow-up motor 13.

Thus the position to which the motor translates telescope tube 3 along its longitudinal or optical axis is an accurate measurement of the location of the corresponding edge of incipient glass ribbon G, laterally with respect to the bath of molten tin T within the furnace, at the selected location. Thus change in position of the edge of ribbon G along the axis of tube 3 may be directly measuredby the translational position of nut element 12, for example, on and along its threaded rod 11. Hence the desired indication of the location of the border or edge of the glass ribbon G in the vertical plane through the optical axis of telescope 3 may be transmitted to a remote control station, by any suitable telemetric means such as a potentiometer, selsyn, bridge circuit, etc. reproducing to a high degree of accuracy the corresponding instantaneous location of nut 12 on and longitudinally along rod 11. It will be understood that the invention contemplates the installment of at least one apparatus such as the one previously described, for each edge or border of the incipient glass ribbon under production. It is also contemplated that several of the apparatuses may be installed, one for each of several critical or significant locations along each edge of the ribbon. Each apparatus so installed may be continuously or intermittently operated and the remote indications of all may be grouped at the aforesaid remote control station. The limits of translation of nut 12 are determined by the effective length of guide rods 6 and 7 and in any event are sufficient to embrace a range covering all widths of ribbon produced in the furnace.

As many modifications, substitutions of equivalents, rearrangement of parts, and variations in mode or manner of operation will readily occur to those skilled in the art, after a study of the foregoing, the disclosure is to be taken in an illustrative rather than a limiting sense. Merely as one example, nut element 12 may have an indicator fixed therewith for cooperation with a linear scale, not shown, adjacent to and parallel with rod 11. Such scale may be engraved on or otherwise carried by and fixed with one of rods 6 or 7.

We claim:

1. Apparatus for the determination at a selected location therealong, of the position of the edge of a ribbon of glass being processed on a bath of molten metal, comprising, means for optically gathering rays emanating from a small area encompassing the edge of the ribbon and the contiguous metal, optical filtering means passing only rays of more than about 4 microns wave length emanating from said area, optical means directing rays from said gathering means to incidence on said filtering means, radiation sensing means responsive essentially only to rays traversing said filtering means of not more than about 8 microns wave length, and means responsive to the signal output of said radiation sensing means to indicate lateral movement of the edge of the ribbon at said location.

2. The apparatus of claim 1, the bath and glass being within an opaque enclosure at the melting temperature of the glass, a telescope tube having an objective end with an observation opening therein above the edge of the glass, means mounting said optical gathering means and filtering means within said tube, and means mounting said tube for' translation transversely of the direction of movement of the ribbon.

3. The apparatus of claim 2, said tube having its longitudinal optical axis parallel with the plane of the ribbon being processed, and generally normal to the direction of movement thereof, there being an observation opening in the objective end of said tube, with axis normal to said plane, said optical observation means including an optical reflector deflecting observed rays entering said opening axially of said tube and onto said filtering means.

4. The apparatus of claim 2, a jacket surrounding said tube in radially-spaced relation therewith, and forming therewith a cooling chamber, and connections for the inlet and exhaust of cooling fluid to and from said chamber.

5. The apparatus of claim 3, said telescope tube comprising first and second coaxial radially-spaced intermediate and inner tubes, said optical observation means and filtering means being mounted in and along the axis of said inner tube, and means connected with said intermediate tube for introducing an inert gas into the space between said tubes, the gas being exhausted through the observation opening in said intermediate tube.

6. Apparatus for the determination at a selected location therealong, of the position of the edge of a ribbon of glass being processed on a bath of molten metal,

comprising, filter means passing only radiant energy above a wavelength of about 4 microns, optical observation means projecting radiant energy emanating from a small area, at said location encompassing the edge of the ribbon and the contiguous molten metal, into incidence on said filter means, photoelectric cell means responsive essentially only to wavelengths of less than about 8 microns and positioned to receive only radiant energy traversing said filter means, indicator means, and circuitry including said photoelectric cell means for controlling said indicator means in accordance with changes in location of said area.

7. The apparatus of claim 6, and synchronouslydriven means for periodically intercepting at a controlled rate, the rays incident upon said photoelectric cell means.

8. The apparatus of claim 6, said ribbon moving on the bath, in the direction of its length, a telescope tube enclosing and supporting said optical observation means, filter means, and photoelectric cell means therein, optically arranged in the order mentioned, means mounting said tube for translation with its longitudinal axis parallel with the plane of the ribbon and generally normal to said direction, a reversible followup motor connected with said tube to so translate the same, said motor being included in said circuitry to be reversely energized by and in response to differential energization of said photoelectric cell means by radiant energy traversing said filter means, said optical observation means being disposed to receive and transmit radiant energy emanating from said area only.

9. The apparatus of claim 8, said longitudinal axis being essentially horizontal, said observation means including an objective reflector diverting observed energy emanating from said area and traversing an opening in said tube, axially along said tube to incidence on said filter means.

10. The apparatus of claim 9, said photoelectric cell means comprising a pair of closely-spaced ray-sensitive elements, said optical observation means and said raysensitive elements being constructed and arranged such that (a) when the edge of the ribbon at said area is in normal desired position, a first one only of said elements is effectively energized, (b) when the edge of the ribbon at said area moves in the direction toward the opposite edge thereof, the rays incident on said elements is thereby augmented to effectively energize both said elements, and (c) when the edge of the ribbon at said area moves in the direction away from the opposite edge thereof, the intensity of rays incident and effective on both said ray-sensitive elements is decreased to thus effectively de-energize said elements, said circuitry operating to rotate said motor in respectively opposite directions under conditions (b) and (c), and to de-energize said motor under condition (a).

11. In the process of forming'a continuous ribbon of molten flat glass and floating it across a bath of molten metal within an opaque enclosure at appropriate high temperature, the method of locating and following the edge of the ribbon inside the enclosure which comprises aligning ray transmitting means with the edge of the incandescent ribbon within the enclosure and transmitting rays toward photosensitive apparatus outside the enclosure, detecting infrared rays of wave length on the order of about 4 to about 8 microns, and using the variations in the output of the photosensitive apparatus derived from variations in the intensity of said infrared rays impinging thereupon to signal changes in position of the edge of the ribbon.

12. In the process of claim 11 the step of concentrating the rays from the ray transmitting means upon a fil ter which interrupts rays of less than about 4 microns wave length.

13. In the process of claim 12 the step of concentrating the rays by means of a fluorspar or fluorite lens system.

14. In the process of claim 11 the step of interposing a moving curtain of inert gas between the ray transmitting means and the incandescent flat glass and molten metal bath.

15. The method of claim 11 in which the ray transmitting means is located in the zone where the incipient ribbon of flat glass approximates its maximum width.

16. The method of claim 11 in which a pair of such ray transmitting means are mounted for operation directly opposite one another, each of which follows the variations in transverse position of an edge of the ribbon.

17. The process of claim 11 in which the variations in output as aforesaid are used to make the ray transmitting means follow the edge of the ribbon in its lateral movement.

18. In the process of claim 12, the step of directing the filtered rays upon photosensitive apparatus which is essentially non-responsive to rays having a wave length above about 8 microns.

19. The method of determining the location of the hidden edge of a moving ribbon of flat glass moving across the surface of a bath of molten metal which comprises isolating the infrared rays of about 4 to about 8 microns wave length emanating from the locus of the edge of the ribbon from the other rays emanating from the bath and the glass, detecting the said isolated rays by photoelectric means isolated from the heat of the glass and bath, and utilizing the variations in output of the photoelectric means to reveal changes in position of the edge of the glass upon the surface of the molten metal bath. 

1. Apparatus for the determination at a selected location therealong, of the position of the edge of a ribbon of glass being processed on a bath of molten metal, comprising, means for optically gathering rays emanating from a small area encompassing the edge of the ribbon and the contiguous metal, optical filtering means passing only rays of more than about 4 microns wave length emanating from said area, optical means directing rays from said gathering means to incidence on said filtering means, radiation sensing means responsive essentially only to rays traversing said filtering means of not more than about 8 microns wave length, and means responsive to the signal output of said radiation sensing means to indicate lateral movement of the edge of the ribbon at said location.
 2. The apparatus of claim 1, the bath and glass being within an opaque enclosure at the melting temperature of the glass, a telescope tube having an objective end with an observation opening therein above the edge of the glass, means mounting said optical gathering means and filtering means within said tube, and means mounting said tube for translation transversely of the direction of movement of the ribbon.
 3. The apparatus of claim 2, said tube having its longitudinal optical axis parallel with the plane of the ribbon being processed, and generally normal to the direction of movement thereof, there being an observation opening in the objective end of Said tube, with axis normal to said plane, said optical observation means including an optical reflector deflecting observed rays entering said opening axially of said tube and onto said filtering means.
 4. The apparatus of claim 2, a jacket surrounding said tube in radially-spaced relation therewith, and forming therewith a cooling chamber, and connections for the inlet and exhaust of cooling fluid to and from said chamber.
 5. The apparatus of claim 3, said telescope tube comprising first and second coaxial radially-spaced intermediate and inner tubes, said optical observation means and filtering means being mounted in and along the axis of said inner tube, and means connected with said intermediate tube for introducing an inert gas into the space between said tubes, the gas being exhausted through the observation opening in said intermediate tube.
 6. Apparatus for the determination at a selected location therealong, of the position of the edge of a ribbon of glass being processed on a bath of molten metal, comprising, filter means passing only radiant energy above a wavelength of about 4 microns, optical observation means projecting radiant energy emanating from a small area, at said location encompassing the edge of the ribbon and the contiguous molten metal, into incidence on said filter means, photoelectric cell means responsive essentially only to wavelengths of less than about 8 microns and positioned to receive only radiant energy traversing said filter means, indicator means, and circuitry including said photoelectric cell means for controlling said indicator means in accordance with changes in location of said area.
 7. The apparatus of claim 6, and synchronously-driven means for periodically intercepting at a controlled rate, the rays incident upon said photoelectric cell means.
 8. The apparatus of claim 6, said ribbon moving on the bath, in the direction of its length, a telescope tube enclosing and supporting said optical observation means, filter means, and photoelectric cell means therein, optically arranged in the order mentioned, means mounting said tube for translation with its longitudinal axis parallel with the plane of the ribbon and generally normal to said direction, a reversible follow-up motor connected with said tube to so translate the same, said motor being included in said circuitry to be reversely energized by and in response to differential energization of said photoelectric cell means by radiant energy traversing said filter means, said optical observation means being disposed to receive and transmit radiant energy emanating from said area only.
 9. The apparatus of claim 8, said longitudinal axis being essentially horizontal, said observation means including an objective reflector diverting observed energy emanating from said area and traversing an opening in said tube, axially along said tube to incidence on said filter means.
 10. The apparatus of claim 9, said photoelectric cell means comprising a pair of closely-spaced ray-sensitive elements, said optical observation means and said ray-sensitive elements being constructed and arranged such that (a) when the edge of the ribbon at said area is in normal desired position, a first one only of said elements is effectively energized, (b) when the edge of the ribbon at said area moves in the direction toward the opposite edge thereof, the rays incident on said elements is thereby augmented to effectively energize both said elements, and (c) when the edge of the ribbon at said area moves in the direction away from the opposite edge thereof, the intensity of rays incident and effective on both said ray-sensitive elements is decreased to thus effectively de-energize said elements, said circuitry operating to rotate said motor in respectively opposite directions under conditions (b) and (c), and to de-energize said motor under condition (a).
 11. In the process of forming a continuous ribbon of molten flat glass and floating it across a bath of molten metal within an Opaque enclosure at appropriate high temperature, the method of locating and following the edge of the ribbon inside the enclosure which comprises aligning ray transmitting means with the edge of the incandescent ribbon within the enclosure and transmitting rays toward photosensitive apparatus outside the enclosure, detecting infrared rays of wave length on the order of about 4 to about 8 microns, and using the variations in the output of the photosensitive apparatus derived from variations in the intensity of said infrared rays impinging thereupon to signal changes in position of the edge of the ribbon.
 12. In the process of claim 11 the step of concentrating the rays from the ray transmitting means upon a filter which interrupts rays of less than about 4 microns wave length.
 13. In the process of claim 12 the step of concentrating the rays by means of a fluorspar or fluorite lens system.
 14. In the process of claim 11 the step of interposing a moving curtain of inert gas between the ray transmitting means and the incandescent flat glass and molten metal bath.
 15. The method of claim 11 in which the ray transmitting means is located in the zone where the incipient ribbon of flat glass approximates its maximum width.
 16. The method of claim 11 in which a pair of such ray transmitting means are mounted for operation directly opposite one another, each of which follows the variations in transverse position of an edge of the ribbon.
 17. The process of claim 11 in which the variations in output as aforesaid are used to make the ray transmitting means follow the edge of the ribbon in its lateral movement.
 18. In the process of claim 12, the step of directing the filtered rays upon photosensitive apparatus which is essentially non-responsive to rays having a wave length above about 8 microns.
 19. The method of determining the location of the hidden edge of a moving ribbon of flat glass moving across the surface of a bath of molten metal which comprises isolating the infrared rays of about 4 to about 8 microns wave length emanating from the locus of the edge of the ribbon from the other rays emanating from the bath and the glass, detecting the said isolated rays by photoelectric means isolated from the heat of the glass and bath, and utilizing the variations in output of the photoelectric means to reveal changes in position of the edge of the glass upon the surface of the molten metal bath. 